The present invention relates to an insulating material for forming the main insulation of an electric machine winding, a rotary electric machine winding and a method for manufacturing the same.
A method for manufacturing an insulating layer of a winding used for a rotary electric machine by winding around a bunch of conductors an insulating material having a mica layer, a reinforcing material layer, and a filler layer including fillers having a high thermal conductivity, wherein these layers contain a thermosetting resin, is described in Japanese Unexamined Patent Application No. 63-110929. This insulating material is wound around the outer peripheral portion of a bunch of winding conductors and the resin in the insulating material is heated and cured while applying pressure thereto to form an insulating layer of the electric machine winding. When the electric machine winding is manufactured, the conductor side is wrapped with the above-mentioned mica and the reinforcing insulating material, and the insulating material layer is impregnated with a thermosetting resin composition containing fine-particle-shaped inorganic fillers and is then pressed, heated, and cured. In this respect, there is described a method for impregnating or applying the thermosetting resin composition containing fillers into or to a mica foil before the winding of a mica foil around the bunch of conductors.
In Japanese Unexamined Patent Application No. 55-53802 is described an insulating material in which an aggregate mica sheet is mixed with synthetic fibers and high-thermal-conductivity inorganic powder and is impregnated with a thermosetting resin. In this connection, in this patent gazette is described an insulating sheet made by bonding a glass cloth to an aggregate mica foil with an epoxy resin.
There is no problem in using an electric machine winding having an insulating layer formed of the above-mentioned insulating material for a rotary electric machine operated at low voltage. However, if the electric machine winding is used for such a rotary electric machine operated at high voltage as an industrial generator or a high-voltage electric machine, there may be cases where it presents a problem in electric characteristics because of an electric defect. The present inventor investigated the cause of the electric defect of the insulating material and found that the electric defect was attributed to part of fine bubbles which were included in the resin of the mica layer, the reinforcing material layer and the filler layer and were not discharged with part of the resin but were left in the insulating material when the insulating layer was wound around a bunch of conductors of the electric machine winding and was formed by pressing. The inventor found that this was caused by the insufficient flow or the unbalanced flow of the impregnated resin produced in a process for pressing, forming, curing the insulating layer of the electric machine winding because the amount of resin in each layer of the mica layer and the filler layer is not kept at a suitable value.
It is an object of the present invention to provide an insulating material capable of producing an insulating layer of an electric machine winding excellent in electric characteristics and an electric machine winding having an insulating layer excellent in electric characteristics.